Heat storage system

ABSTRACT

A heat storage system includes an energy conversion portion, and a heat storage portion having a heat storage material. The energy conversion portion converts a form of an energy source into another form, and the energy conversion portion dissipates heat through a medium at the same time as the energy conversion. The heat storage material exchanges heat with the medium. The heat storage material stores heat from the medium in a heat storage mode, and the heat storage material dissipates the stored heat to a heating target. The heat storage material exhibits a first solid phase when a temperature of the heat storage material is higher than a predetermined temperature, and the heat storage material exhibits a second solid phase when the temperature of the heat storage material is at or lower than the predetermined temperature.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on and incorporates herein by reference Japanese Patent Application No. 2015-161617 filed on Aug. 19, 2015.

TECHNICAL FIELD

The present disclosure relates to a heat storage system.

BACKGROUND ART

In an energy conversion system such as a cogeneration, a spatial-temporal gap is likely to occur between a time when heat is excessive (normal time) and a time when heat is required (starting time). Accordingly, there is a known technology, in which a part of heat dissipated from an energy conversion portion is stored in the normal time, and the stored heat is dissipated in the starting time.

For example, Patent Document 1 discloses a heat storage device in which a solid-liquid phase transition material is used as a heat storage material. The heat storage material stores heat by using the phase transition during condensation and melting. Specifically, the heat storage material is enclosed in a casing, and a circulating water exchanges heat with the heat storage material through the casing. The casing limits runoff of the liquid of the heat storage when the heat storage material changes its phase from solid to liquid during the heat storage.

A heat storage material that exhibits such phase transition may be used in a heat storage device of a cogeneration system, for example.

PRIOR ART DOCUMENT Patent Document

Patent Document 1: JP 2011-068190 A

SUMMARY OF THE INVENTION

However, in the above-described conventional technology, the casing may function as a large thermal resistance, and accordingly a large heat transfer area may be required for obtaining a predetermined heat output. Consequently, a size of a heat storage tank may be excessively large.

In consideration of the above-described points, it is an objective of the present disclosure to provide a heat storage system that does not need a casing for accommodating a heat storage material.

A heat storage system according to an aspect of the present disclosure includes an energy conversion portion, and a heat storage portion having a heat storage material. The energy conversion portion converts a form of an energy source into another form, and the energy conversion portion dissipates heat through a medium at the same time as the energy conversion. The heat storage material is configured to exchange heat with the medium, and the heat storage material stores heat from the medium in a heat storage mode. The heat storage material dissipates the stored heat to a heating target in a heat dissipation mode different from the heat storage mode. The heat storage material is in a first solid phase when a temperature of the heat storage material is higher than a predetermined temperature, and the heat storage material is in a second solid phase when the temperature of the heat storage material is equal to or lower than the predetermined temperature.

According to this, the heat storage material maintains a solid phase even after phase transition of the heat storage material of the heat storage portion. Accordingly, a casing for maintaining a shape of the heat storage material can be omitted.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram illustrating configurations of a heat storage system according to a first embodiment of the present disclosure.

FIG. 1B is a diagram illustrating configurations of the heat storage system according to the first embodiment.

FIG. 2 is a phase diagram of a heat storage material.

FIG. 3 is a diagram illustrating configurations of a heat storage system according to a second embodiment of the present disclosure.

FIG. 4 is a diagram illustrating a heat storage material according to a second embodiment of the present disclosure.

FIG. 5 is a diagram illustrating a heat storage material according to a third embodiment of the present disclosure.

FIG. 6 is a diagram illustrating a heat storage material according to a fourth embodiment of the present disclosure.

FIG. 7 is a diagram illustrating a heat storage material according to a fifth embodiment of the present disclosure.

FIG. 8 is a diagram illustrating a heat storage material according to a sixth embodiment of the present disclosure.

FIG. 9 is a diagram illustrating a heat storage material according to a seventh embodiment of the present disclosure.

FIG. 10 is a diagram illustrating a heat storage material according to a eighth embodiment of the present disclosure.

FIG. 11 is a diagram illustrating a heat storage material according to a ninth embodiment of the present disclosure.

EMBODIMENTS FOR EXPLOITATION OF THE INVENTION

Hereinafter, multiple embodiments for implementing the present disclosure will be described referring to drawings. In the respective embodiments, a part that corresponds to a matter described in a preceding embodiment may be assigned the same reference numeral, and redundant explanation for the part may be omitted. When only a part of a configuration is described in an embodiment, another preceding embodiment may be applied to the other parts of the configuration. The parts may be combined even if it is not explicitly described that the parts can be combined. The embodiments may be partially combined even if it is not explicitly described that the embodiments can be combined, provided there is no harm in the combination.

First Embodiment

A first embodiment of the present disclosure is described below with reference to the drawings. A heat storage system according to the present embodiment is used in a cogeneration system that stores heat to use the stored heat.

The heat storage system includes an energy conversion portion 10 and a heat storage portion 20 as shown in FIGS. 1A and 1B. The energy conversion portion 10 converts a form of energy of an energy source into another form, and the energy conversion portion 10 dissipates heat through a predetermined medium at the same time as the energy conversion.

For example, in a vehicle, the energy conversion portion 10 is a fuel cell, an engine or the like. The energy source is a fuel, and another form of energy is a driving force, an electric power or the like. The predetermined medium is a cooling water, an exhaust gas or the like.

The heat storage portion 20 includes a heat storage material. The heat storage material is capable of exchanging heat with the medium. The heat storage portion 20 stores heat in the heat storage material from the medium in a heat storage mode, and the heat storage portion 20 dissipates the heat stored in the heat storage material to a heating target in a heat dissipation mode different from the heat storage mode.

As shown in FIG. 2, the heat storage material is in a first phase that is a solid phase when a temperature of the heat storage material is higher than a predetermined temperature, and the heat storage material is in a second phase that is a solid phase when the temperature of the heat storage material is at or below the predetermined temperature. The heat storage mode corresponds to a time period when the temperature of the heat storage material is higher than the predetermined temperature, and the heat dissipation mode corresponds to a time period when the temperature of the heat storage material is equal to or lower than the predetermined temperature. The heat storage material stores heat from the medium in the heat storage mode, and the heat storage material dissipates the stored heat in the heat dissipation mode. The heat storage material exhibits solid-solid phase transition in a cycle of the heat storage mode and the heat dissipation mode, and the heat storage material keeps being in solid phase.

The heat storage material is made of vanadium dioxide (VO₂) that is a strongly correlated electron material, for example. The predetermined temperature, i.e. a phase transition temperature, is adjusted by the amount of additive doped to vanadium dioxide. For example, the larger the doping amount of the additive is, the higher the predetermined temperature is.

According to the above-described configurations, in FIG. 1A, the heat is stored in the heat storage material when the temperature of the cooling water that is the medium is higher than the predetermined temperature, and the heat is dissipated from the heat storage material when the temperature of the heat storage material is lower than the predetermined temperature. In contrast, in FIG. 1B, the heat is stored in the heat storage material when the temperature of the exhaust gas that is the medium is higher than the predetermined temperature, and the heat is dissipated from the heat storage material when the temperature of the heat storage material is lower than the predetermined temperature.

As described above, the present disclosure is characterized in that the heat storage portion 20 is constituted by using the heat storage material that exhibits solid-solid phase transition. According to this, since the heat storage material maintains solid-phase after the phase transition, a casing for maintaining a shape of the heat storage material can be omitted. Accordingly, a thermal resistance of the casing is removed, and an increase in size of the heat storage portion 20 can be limited.

Second Embodiment

In the present embodiment, parts different from the first embodiment are described. In the present embodiment, a heat storage tank is used as an example of the heat storage system.

As shown in FIG. 3, a circulating water is introduced to a heat storage tank 30 from a lower part of a body portion 32 through one pipe 31, and the circulating water is discharged from an upper part of the body portion 32 through another pipe 33. Available water flows into and out of the body portion 32 from a lower part thereof. When the heat storage tank 30 is used as the heat storage system, the energy conversion portion 10 is a water heater that heats water, for example. The energy source is electricity, and another form of the energy is heat. The predetermined medium is the circulating water.

The heat storage material is accommodated in the body portion 32 of the heat storage tank 30. As shown in FIG. 4, a heat storage material 40 has a block shape. The heat storage material 40 includes multiple through-holes 41 extending along one direction. That is, the heat storage material 40 has a flow-through honeycomb structure. On an end surface of the heat storage material 40, the multiple through-holes 41 are arranged in a square array. The shape of the through-hole 41 is not limited to a quadrilateral, and the shape may be a polygon, a circle, or an ellipse.

Accordingly, when the circulating water flows along an outer wall surface or flows through the multiple through-holes 41, the heat storage material 40 stores heat of the circulating water or dissipates heat to the circulating water. The multiple through-holes increase the surface area of the heat storage material 40. Accordingly, the thermal conductivity of the heat storage material 40 can be improved. Since a flow of the circulating water can be straightened, a desired heat storage amount can be obtained.

Third Embodiment

In the present embodiment, parts different from the second embodiment are described. In the present embodiment, the multiple through-holes 41 of the heat storage material 40 are arranged in a hexagonal lattice shape on the end surface of the heat storage material 40, as shown in FIG. 5. According to this, a strength of the heat storage material 40, in which the through-holes 40 are provided, can be secured.

Fourth Embodiment

In the present embodiment, parts different from the second and third embodiments are described. As shown in FIG. 6, the multiple through-holes 41 of the heat storage material 40 are arranged in a Fibonacci spiral on the end surface of the heat storage material. According to this, both a strength and a surface area of the heat storage material 40 can be secured.

Fifth Embodiment

In the present embodiment, parts different from the second to fourth embodiments are described. As shown in FIG. 7, the heat storage material 40 has a pack-head structure in which multiple blocks 42 are stacked with predetermined gaps.

The shape of the block 42 is a cuboid, for example. The shape of the block 42 may be a sphere shape (bead shape) or a lens shape, for example. When the block 42 has a sphere shape, a clearance between the blocks 42 can be controlled by adjusting an aspect ratio.

Sixth Embodiment

In the present embodiment, parts different from the fifth embodiment are described. As shown in FIG. 8, the heat storage material 40 is constituted by a combination of comb-shaped blocks 42. According to this, since a surface area of the heat storage material 40 is large, the thermal conductivity of the heat storage material 40 can increase. Multiple pairs of the heat storage materials 40 having comb shapes may be aligned.

Seventh Embodiment

In the present embodiment, parts different from the second to sixth embodiments are described. As shown in FIG. 9, the heat storage material 40 has a plate structure, in which multiple plates 43 are arranged at predetermined intervals. According to this, the heat storage material 40 can be easily manufactured.

Eighth Embodiment

In the present embodiment, parts different from the seventh embodiment are described. As shown in FIG. 10, the plate 43 constituting the heat storage material 40 may have a wavy shape. According to this, a surface area of the heat storage material 40 can be large.

Ninth Embodiment

In the present embodiment, parts different from the seventh embodiment are described. As shown in FIG. 11, the plate 43 constituting the heat storage material 40 may have multiple punched holes 44. According to this, a surface area of the heat storage material 40 can be large. Moreover, the circulating water can move through the plates 43.

Configurations of the heat storage system of the above-described embodiments are just examples, and the configurations are not limited to those as far as the configurations can achieve the objective of the present disclosure. For example, the heat storage system is not limited to be used in a vehicle or a water heater. The shape of the heat storage material 40 may be a shape other than the above-described shapes.

Although the present disclosure has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art. Moreover, other combinations and configurations, including more, less or only a single element, are also within the spirit and scope of the present disclosure. 

What is claimed is:
 1. A heat storage system comprising: an energy conversion portion that converts a form of an energy source into another form, the energy conversion portion dissipating heat through a medium at a same time as the energy conversion; and a heat storage portion that includes a heat storage material configured to exchange heat with the medium, the heat storage material storing heat from the medium in a heat storage mode, the heat storage material dissipating the stored heat to a heating target in a heat dissipation mode different from the heat storage mode, wherein the heat storage material is in a first solid phase when a temperature of the heat storage material is higher than a predetermined temperature, and the heat storage material is in a second solid phase when the temperature of the heat storage material is equal to or lower than the predetermined temperature.
 2. The heat storage system according to claim 1, wherein the heat storage material has a flow-through honeycomb structure in which a plurality of through-holes extend along one direction.
 3. The heat storage system according to claim 1, wherein the heat storage material has a pack-head structure in which a plurality of blocks are stacked with each other at predetermined intervals.
 4. The heat storage system according to claim 1, wherein the heat storage material has a plate structure in which a plurality of plates are arranged at predetermined intervals.
 5. The heat storage system according to claim 1, wherein the heat storage material is made essentially of vanadium dioxide.
 6. The heat storage system according to claim 5, wherein the heat storage material includes an additive, and the predetermined temperature varies depending on an amount of the additive doped to the vanadium dioxide.
 7. The heat storage system according to claim 1, wherein the heat storage mode corresponds to a time period when the temperature of the heat storage material is higher than the predetermined temperature, and the heat dissipation mode corresponds to a time period when the temperature of the heat storage material is equal to or lower than the predetermined temperature. 